What is the approach to diagnose acute diffuse abdominal pain?

Diagnostic Approach to Acute Diffuse Abdominal Pain

For acute diffuse (nonlocalized) abdominal pain, CT of the abdomen and pelvis with IV contrast is the imaging modality of choice when serious pathology is suspected or the diagnosis remains unclear after initial assessment. 1, 2

Initial Clinical Assessment

Vital Signs and Physical Examination

• Evaluate for tachycardia first—this is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 3, 2, 4
• Assess for the triad of fever, tachycardia, and tachypnea, which predicts serious complications including anastomotic leak, perforation, or sepsis 3, 2
• Check for hypotension or signs of shock, which suggest bleeding or sepsis 3
• Look for peritoneal signs (rigid abdomen, rebound tenderness), though their absence does not exclude bowel ischemia—patients with sigmoid volvulus often lack peritoneal signs despite established ischemia due to chronic distension masking the examination 3, 2
• Severe pain out of proportion to physical examination findings is pathognomonic for acute mesenteric ischemia and requires immediate investigation 3, 2, 4

History Elements

• Document symptom duration, onset (sudden vs. gradual), and character (colicky pain suggests bowel obstruction) 3
• Ask about last bowel movement and passage of gas—this has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction in patients with prior abdominal surgery 3
• Inquire about vomiting pattern (earlier and more prominent in small bowel obstruction) 3
• Review surgical history—any prior laparotomy makes adhesive obstruction the leading diagnosis, accounting for 55-75% of small bowel obstructions 3
• Assess for medications affecting peristalsis, particularly psychotropic drugs that cause chronic constipation predisposing to volvulus 3

Mandatory Laboratory Testing

Essential Tests

• Beta-hCG testing is mandatory in all women of reproductive age before any imaging to rule out ectopic pregnancy 3, 2, 4
• Complete blood count to evaluate for leukocytosis suggesting infection or inflammation 3, 2, 4
• C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 3, 2
• Comprehensive metabolic panel including liver function tests 4
• Serum lipase for suspected pancreatitis 4
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 4

Additional Tests When Indicated

• Elevated lactate suggests ischemia or sepsis, but normal levels do not exclude internal herniation or early ischemia 3, 2
• Procalcitonin is helpful for assessing inflammatory response in suspected sepsis 3
• D-dimer if mesenteric ischemia is suspected 3

Imaging Strategy

Primary Imaging Recommendation

CT of the abdomen and pelvis with IV contrast is the optimal imaging choice for acute nonlocalized abdominal pain, particularly when fever is present or serious pathology is suspected 1, 2, 4

• This modality changes the leading diagnosis in 49-51% of patients and alters the management plan in 42% of patients 1, 4
• It provides comprehensive evaluation of the broad differential diagnosis associated with diffuse pain 1, 2

Alternative Imaging Considerations

• Conventional radiography has limited diagnostic value in most patients with abdominal pain and should not be routinely ordered 1, 4
• Plain radiography may be appropriate only for suspected bowel obstruction, perforated viscus, urinary tract calculi, or foreign bodies 1
• MRI is an emerging technique that avoids ionizing radiation but is less readily available 1

Specific Imaging for Suspected Conditions

• Bowel obstruction: CT abdomen and pelvis with contrast 3
• Mesenteric ischemia: CT angiography of the abdomen 3
• Suspected kidney stones: Non-contrast CT abdomen and pelvis 3, 2

Special Population Considerations

Women of Reproductive Age

• Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease 3, 2, 4
• CT of the abdomen and pelvis with contrast is most appropriate for pelvic pain 3, 2, 4

Elderly Patients

• Have a higher likelihood of malignancy, diverticulitis, and vascular causes 3, 2, 4
• May present with atypical symptoms and require more thorough evaluation even if laboratory tests are normal 3, 2, 4
• Many laboratory tests may be normal despite serious infection 2, 4

Post-Bariatric Surgery Patients

• Often present with atypical symptoms, and classic peritoneal signs are frequently absent 3, 2
• Tachycardia is the most critical warning sign in this population 3
• Consider internal herniation even with normal lactate 3

Critical Pitfalls to Avoid

• Failing to obtain β-hCG testing in women of reproductive age before imaging can delay diagnosis of life-threatening ectopic pregnancy 4
• Normal lactate does not exclude internal herniation or early ischemia 3, 2
• The absence of peritonitis on examination does not exclude bowel ischemia 3, 2
• Normal laboratory tests in elderly patients do not exclude serious infection 2, 4
• Avoid overuse of CT scans to minimize ionizing radiation exposure, especially in young patients, though this should not delay necessary imaging 3

Red Flags Requiring Urgent Evaluation

• Severe pain out of proportion to physical findings (mesenteric ischemia) 3, 2
• Signs of peritonitis (rigid abdomen, rebound tenderness) 3
• Hemodynamic instability suggesting bleeding or sepsis 3
• Fever with abdominal pain suggesting infection or abscess 3
• Abdominal distension with vomiting suggesting bowel obstruction 3
• The combination of fever, tachycardia, and tachypnea 3, 2